Fully coupled modeling of burnup dependent (U_1-y, Pu_y)O_2-x fast reactor fuel performance

During the fast reactor nuclear fuel fission reaction, fission gases accumulate and form pores with the increasing of fuel burnup that decrease the fuel thermal conductivity, leading to overheating of the fuel element. The diffusion of plutonium and oxygen with high temperature gradient is also one of the important fuel performance concerns as it will affect fuel materials properties, power distribution and overall performance of the fuel pin. In order to investigate these important issues, we study the (U_1-yPu_y)O_2-x fuel pellet by fully coupling the thermal transport, thermal expansion, oxygen diffusion, fission gas release and swelling and plutonium redistribution to evaluate the effects on each other with a burnup dependent thermal conductivity model, which accounts for the evolution of fuel porosity. We find the radial temperature and deformation profiles are most sensitive to O/M ratio at small values of plutonium content. For larger values of plutonium content, the effects of O/M ratio and plutonium content are equally important, which is the same results to the previous modeling work even though based on different material properties' models. Additionally, the porosity is found to be very sensitive to fuel temperature at the beginning of fuel burnup, while the fuel burnup profile dominates the degradation fuel thermal conductivity during the whole fuel irradiation. (author)